The cohort study is designed to measure the individual risks and benefits of menopausal estrogen therapy in terms of incident disease and mortality; to study whether longterm use of Vitamin A supplements alters risk to epithelial cancers; and to evaluate the possible risks and benefits associated with other 'health related' practices in older adults. Questionnaires will be mailed to all 19,800 residents of a retirement community in Orange County, California, requesting information on use of estrogen replacement therapy (women only), on use of vitamin supplements, and on other health-related practices, including cigarette smoking, alcohol consumption, exercise habits, intake of certain dietary nutrients or food items (Vitamin A and Vitamin C, coffee, artificial sweeteners) and use of periodic screening for certain chronic diseases. Non-respondents will be mailed three such questionnaires in all and then be contacted by telephone. In this way, we expect to identify a cohort of 14,000 persons. Follow-up will be maintained by annual recontact of each surviving cohort member; by routine ascertainment of death certificates from the Orange County Health Department, and by routine screening of disease indices of all local hospitals.